StarDate Podcast

Antares is a rare star. It’s one of the few named for what it’s not. The name is Greek. It combines “anti,” which means “against” or “opposed to” – with Ares – the Greek version of Mars, the god of war. So the name means “not Mars” or “rival of Mars.” It was given the name because its color is similar to that of Mars – bright orange. The color indicates that the surface of Antares is thousands of degrees cooler than the surface of the Sun. Cooler stars glow red or orange, while hotter stars are white or blue. Antares is one of many designations for the star. Because it’s the brightest star of Scorpius, it’s also known as Alpha Scorpii. And it’s also called the heart of the scorpion – Cor Scorpii. Antares also has designations in many catalogs – lists of stars that have something in common. It’s in the bright-star catalog as HR 6134. It has a companion star, so it’s in the binary-star catalog. And it’s in several catalogs of objects that produce a lot of infrared light. In all, Antares has dozens of names and catalog numbers – an impressive list for an impressive star. The gibbous Moon slips past Antares the next couple of mornings. The star will be to the left or lower left of the Moon at dawn tomorrow. And it will stand a little closer to the upper right of the Moon on Wednesday. Tomorrow: more stars for the Pleiades. Script by Damond Benningfield

Family members don’t always stay close together – they can be separated by thousands of miles. But one member of the Milky Way Galaxy’s family takes the separation to extremes. It’s 300,000 light-years from the center of the galaxy – one of the most distant residents of the Milky Way yet seen. NGC 2419 is a globular cluster – a group of about a million stars. They form a dense ball a few hundred light-years across. Any star near the middle of the cluster would have thousands of neighbors within a few light-years. Compare that to our own neighborhood – only three stars reside less than five light-years from the Sun. NGC 2419 is one of the Milky Way’s oldest family members. The cluster was born more than 12 billion years ago – not long after the galaxy itself. All of its big, bright stars burned out long ago. So almost all of the remaining stars are much less massive than the Sun. The cluster follows a highly stretched-out orbit around the center of the Milky Way. That’s led to suggestions that it was born elsewhere, then captured by the Milky Way. But there’s no confirmation of that idea. So NGC 2419 is still considered a far-away relative of the rest of the Milky Way. The cluster is in the uber-faint constellation Lynx, which is in the east-northeast at nightfall. NGC 2419 is an easy target for just about any telescope. Script by Damond Benningfield

Alpha Lyncis is only about a third of the age of the Sun. Yet the star has already zoomed through the prime phase of life. Now, it’s nearing the end of its life. And it’s letting us know about it – it’s the brightest star of the constellation Lynx. That’s not necessarily saying much. Lynx is a large constellation, but it’s faint – only a few of its stars are bright enough to see from light-polluted cities or suburbs. In fact, the astronomer who created it, in the 1600s, called it “Lynx” because you needed the eyes of one to see it. Alpha Lyncis is classified as a red giant. It’s about half-again the mass of the Sun. Heavier stars age more quickly. Such a star “burns” through the original hydrogen in its core in a hurry. As the core adjusts to the change, the star’s outer layers puff up. Today, Alpha Lyncis is more than 50 times the diameter of the Sun. As it got bigger, the star got cooler and redder – making it a red giant. Puffing up also made the star hundreds of times brighter than the Sun. So Alpha Lyncis is visible – faintly – even though it’s a little more than 200 light-years away. That makes it one of the few stars in this faint constellation that you don’t need the eyes of a lynx to see. Lynx is well up in the east-northeast at nightfall. It’s about half way between the Big Dipper and the twins of Gemini. But you need nice, dark skies to see much. More about the constellation tomorrow. Script by Damond Benningfield

The Moon snuggles close to the bright star Spica late tonight. They climb into good view by about midnight, and are high in the sky at dawn. At their closest, they’ll be separated by just a couple of degrees – about the width of your finger held at arm’s length. That closeness is just an illusion – the Moon and the star are separated by a vast gulf. The Moon is our closest neighbor. Tonight, it’s a little less than a quarter of a million miles away. At that distance, sunlight reflecting from the lunar surface takes about one and a third seconds to reach Earth. That means we see the Moon as it looked one and a third seconds earlier. The Moon is moving farther from us – by an inch and a half per year. That’s a result of the tides. Earth and Moon exert a gravitational grip on each other. That slows Earth’s rotation, making the days a little longer. To balance the books, the Moon moves farther away. Spica is more than nine billion times farther than the Moon. Its light takes about 250 years to reach Earth – the star is 250 light-years away. So as you look at Spica tonight, you’re actually seeing the bright star as it looked 250 years ago – about the time of the American Revolution. And it’s moving away as well – by about 60 million miles per year. That’s a result of Spica’s motion around the center of the galaxy – an orbit that’s carrying the brightest star of Virgo into the distance. Script by Damond Benningfield

The star cluster M79 is messy. It’s shedding some of its stars, creating a “tail.” Over the eons, in fact, the cluster might have lost most of the stars it was born with. Messier 79 is a globular cluster – a ball-shaped family of about 150,000 stars. The cluster is more than 11 billion years old, so its stars are among the oldest in the entire Milky Way Galaxy. There’s a trail of stars behind the cluster. The stars probably were stripped away by the gravity of the rest of the galaxy – especially its dense core. Today, M79 is about 42,000 light-years from the Milky Way’s heart. But its orbit might bring it within just a few hundred light-years of the center. At that distance, the gravity of the galaxy’s core overpowers the gravity of the cluster. So stars in M79’s outskirts are pulled away. Eventually, they move away, and follow their own paths across the galaxy. Some simulations have suggested that M79 has lost up to 85 percent of its original population of a million stars or so. And every future passage through the heart of the galaxy will pull away more stars – leaving only a glimmer of M79’s original glory. M79 is in Lepus, the hare. The constellation is close to the lower right of bright Orion, in the southeast at nightfall. M79 is below the outline of the rabbit. You need binoculars to pick it out. Script by Damond Benningfield

In 1845, British astronomer J.R. Hind saw an amazing star in the constellation Lepus, the rabbit. He wrote that the star looked “like a drop of blood on a black field.” Officially, the star is called R Leporis. But it’s also known as Hind’s Crimson Star – a star that looks redder than almost any other star in the galaxy. R Leporis is a little heavier than the Sun. But it’s much later in life, which makes it a lot more interesting. It’s “fused” the original fuel in its core to make oxygen and carbon. Today, it’s producing energy in shells of hydrogen and helium around the core. Those changes have caused the star’s outer layers to puff up, so R Leporis is hundreds of times the Sun’s diameter. But those layers are unstable. They pulse in and out like a beating heart. Each “beat” lasts about 14 and a half months. During that cycle, the star’s brightness varies dramatically; at its peak, it’s hundreds of times brighter than at its faintest. As the star pulses, its temperature changes. At its largest, it’s a bit cooler, so it looks redder. And that color is amped up by the material in its outer layers. Carbon is pulled up from deep inside the star. It absorbs blue wavelengths of light, allowing the red to shine through – enhancing the “bloody” look of Hind’s Crimson Star. Lepus is in the southeast in early evening, to the lower right of Orion. But you need a telescope to see Hind’s Crimson Star. Script by Damond Benningfield

The brightest star of the rabbit is a member of a rare class. It’s a yellow supergiant – a star that’s about the same color as the Sun, but much bigger and brighter. It won’t stay in that class for long, though. It’ll quickly get hotter and bluer, then blast itself to bits as a supernova. Arneb is the leading light of the constellation Lepus, the hare. It’s in the southeast at nightfall, to the lower right of brilliant Orion. Its name is Arabic for hare – a name that also represented the whole constellation. Arneb is about a dozen times the mass of the Sun, perhaps a hundred times its diameter, and tens of thousands of times its brightness. The star is about 13 million years old – compared to four and a half billion years for the Sun. But because of its great mass, Arneb has already completed the main phase of life. Changes in its core caused it to puff up to become a red supergiant. Now, it’s getting smaller, which is making its surface hotter. As part of that transition, it’s turned yellow. But it won’t stay that color for long. As it continues to contract, it’ll get even hotter, so its surface will turn blue. And within a couple of million years, Arneb will explode. That will leave only a small, superdense core – a neutron star. It’ll be surrounded by an expanding cloud of debris that will shine for millennia – the final act of a rare and mighty star. We’ll have more about the rabbit tomorrow. Script by Damond Benningfield

From parts of the U.S., the Moon will briefly cover the heart of the lion tonight. The Moon will pass directly between Earth and the bright star Regulus, creating an occultation. The Moon can occult Regulus because the star lies almost atop the ecliptic – the Sun’s path across the sky. The Moon stays close to the ecliptic, but it does move a little to either side. So occultations of Regulus come in groups. This one is part of a cycle that began last July and will continue through the end of this year. The occultations are separated by about 27 days, which is how long it takes the Moon to circle through the background of stars. Each occultation is visible from a different part of Earth. In part, that’s because the Moon and Regulus are below the horizon as seen from much of the world. And the Moon is so close to us that there’s a big difference in the viewing angle across the globe. So from any specific location, sometimes the angle is just right, but more often it’s a little off. This month, the angle is right for skywatchers in the eastern United States. For most of the rest of the country, the Moon will just miss the star. So all of us will see an amazingly close encounter between the Moon and the heart of the lion. Only one more occultation in this sequence will be visible from anywhere in the contiguous United States – on April 25th. After that, we won’t see another one until 2044. Script by Damond Benningfield

Odd little February is the shortest month of the year. Historians aren’t exactly sure just why that’s the case. But tracing its evolution gives us a capsule history of the evolution of the calendar. The modern western calendar is a descendant of the earliest Roman calendar. It included only 10 months, beginning with March. The months were followed by about 60 days that weren’t part of any month. That system didn’t work very well, though, so two months were added to the end of the year – January and February. Eventually, they were shifted to the start of the year. The lengths of the 10 original months were changed to leave 56 days for the newcomers. But the Romans feared even numbers, so they added a day to January to give it 29. February was the month for festivals of repentance and for honoring the dead, so it stayed an unlucky even number. But this version of the calendar contained only 355 days. So an extra month was added every other year. In those years, the last five days of February were dropped. After that, February remained unchanged until 46 B.C., when Julius Caesar introduced the basic calendar that’s in use today. He named the seventh month for himself: July. And he might have lengthened February to 29 days. If so, it was cut back to 28 by Augustus Caesar, who took the extra day for the month that bears his name: August. Script by Damond Benningfield

Powerful cold fronts move across North America at this time of year. These blankets of dry, cold air push away the clouds and haze, providing some amazingly beautiful blue skies. That color is produced by the interaction of sunlight with Earth’s atmosphere. The Sun is classified as a yellow star because its energy output peaks at yellow wavelengths. And if we could see the Sun from a distance of a few light-years, where it would appear as only a pinpoint of light, it would have a yellow hue. But from close range, the Sun is so intensely bright that we see its light as a mixture of all the colors of the rainbow. As a result, it looks white. As the Sun’s light enters Earth’s atmosphere, it’s subjected to a number of effects. Most of the time, the most important effect is Rayleigh scattering. It’s named for a British scientist who studied the effect in the late 19th century. Blue light waves are shorter than waves of red light. That makes them the right size to bounce off molecules of nitrogen and oxygen in the atmosphere. That scatters them in random directions. Since the blue wavelengths are scattered across the entire sky, the sky looks blue. Molecules in the air actually scatter a lot of violet light as well. But our eyes are more sensitive to blue wavelengths, so we see the sky as distinctly blue – the frosty color of clear winter days. Tomorrow: the oddball month of February. Script by Damond Benningfield

The constellation Gemini consists of two long lines of stars capped by two of the brighter stars in the night sky. Many cultures have seen these stars as two men. But the legend that endures is the Greek story of Castor and Pollux. The two bright stars bear their names. In the story, the twins had the same mother – Leda, the queen of Sparta. But they had different fathers. Castor was the son of the king – a mortal – while Pollux was the son of Zeus, the king of the gods. The boys were inseparable. They had many adventures together. They joined Jason and the other Argonauts in the search for the golden fleece, and saved their legendary boat during a nasty storm. But during a later battle, Castor was killed. Pollux was inconsolable. He begged Zeus to let him die so he could join Castor in the underworld. Moved by Pollux’s love for his brother, Zeus agreed to keep them together for all time. They would spend half of their time in the heavens, and the other half in the underworld – just like the stars of Gemini. The twins appear near the Moon the next couple of nights. The Moon aligns along the body of the twins tonight. Castor, the fainter twin, is to the left of the Moon at nightfall, with Pollux to the lower left. The giant planet Jupiter is passing through the constellation as well. It looks like an especially brilliant star. Tonight, it’s a little closer to the Moon than the twins are. Script by Damond Benningfield

Gene Cernan was the last American to walk on the Moon. As he prepared to leave it, he expressed optimism that his colleagues would return soon. CERNAN: As I take man’s last step from the surface for some time to come, but we believe not too long into the future… Well, it’s probably been a little longer into the future than Cernan expected, but NASA is preparing to send astronauts back to the Moon. The Artemis II mission is scheduled to launch in the coming weeks. It will carry four astronauts to the Moon. They won’t land, or even go into orbit. But it will be the first time anyone has come close to the Moon in more than half a century. The astronauts will follow a looping path to the Moon. They’ll fly behind it, coming within about 6500 miles of the surface. The Moon’s gravity will sling them back toward Earth. They’ll splash down in the Pacific Ocean. During the 10-day mission, the astronauts will check out all of the systems on the Orion spacecraft. They’ll also conduct a few experiments, and make some observations of the Moon. Artemis II has been delayed by several years. Among other problems, during the unmanned Artemis I mission, in 2022, the life support system and heat shield didn’t work as planned. Astronauts are supposed to land on the Moon during the next mission. Issues with the lander and other problems may delay that until 2028 or beyond – adding to the gap between moonwalks. Script by Damond Benningfield

The Moon is a tale of two faces. The side we see – the nearside – features giant volcanic plains and a fairly thin crust. The far side features more mountains and craters and much thicker crust. And the differences might go even deeper. The layer below the crust – the mantle – might be cooler on the farside – or was cooler billions of years ago. That difference is suggested by samples returned to Earth by a Chinese lander – the first samples from the farside. Some of the samples formed from molten rock. It cooled and solidified 2.8 billion years ago, deep inside the Moon. Details about the samples suggest the molten rock was much cooler than the same layer on the nearside – by about 200 degrees Fahrenheit. That’s probably because the far side has fewer radioactive elements, which heat the interior as they decay. Just why that’s the case isn’t clear. A smaller moon might have splatted into the lunar farside when the Moon was young. Or a giant asteroid impact might have moved things around. The pull of Earth’s gravity might have played a role as well. Whatever the cause, there’s a big difference in the lunar hemispheres – which may be more than skin deep. The gibbous Moon is passing through the constellation Taurus tonight. Aldebaran, the bull’s eye, is to the right of the Moon at nightfall. And Elnath, at the tip of one of the bull’s horns, is closer to the lower left of the Moon. Script by Damond Benningfield

In Greek mythology, Chiron was the wisest of the centaurs – creatures who were half human and half horse. He taught other centaurs about medicine, botany, and other sciences. Today, the astronomical Chiron is teaching scientists about the formation and evolution of ring systems. Chiron is one of about a thousand known centaurs – chunks of ice and rock between the orbits of Jupiter and Neptune. It’s one of the larger ones, at an average diameter of about 125 miles. Even so, it’s so far away that it’s tough to study. But it sometimes passes in front of a distant star. Such a passage allows scientists to measure its size. It also allows them to study the space around Chiron. Rings cause the light of the background star to flicker. Observing that effect from different locations, and at different times, provides a profile of the rings. A study last year reported some changes. Scientists already knew of three rings. The new study reported evidence of a fourth ring. It’s so far out that Chiron’s weak gravity might not be able to hold it. The scientists also found a wide disk of dust. The rings and disk might be debris from a small moon, or the result of an outburst from Chiron itself. Chiron is moving closer to the Sun. As it warms up, it could produce more outbursts. So the system could undergo more big changes in the years ahead – teaching us much more about the evolution of rings around the small bodies of the solar system. Script by Damond Benningfield

The realm of the giant outer planets is like a transit station for some smaller bodies. They come from beyond the orbit of Neptune, the solar system’s most remote major planet. And like passengers at a hub airport, their destinations are all over the map. These objects are called centaurs. Like the half-human, half-horses of myth, they’re hybrids – they look like both asteroids and comets. Most of them are quiet chunks of rock and ice, like asteroids. But some have haloes or tails of gas, like comets. Centaurs orbit the Sun between Jupiter and Neptune. And their orbits cross those of at least one of the giant planets. They’re small and far away, so they’re hard to find. Even so, astronomers have discovered about a thousand of them. And there could be as many as a hundred thousand that are at least a kilometer across. Centaurs come from a belt of debris beyond Neptune. They’re nudged inward by Neptune’s gravity. None of them will spend more than a few million years in the realm of the giants, though. Instead, the gravity of the planets will give them a kick. Some will be booted out of the solar system. Others will be pushed into the inner solar system. And others will slam into a planet. The biggest centaur is Chariklo. It’s about 160 miles in diameter, and it has a couple of rings. The first centaur ever seen, Chiron, also has rings. And it’s growing new rings even now. More about that tomorrow. Script by Damond Benningfield

Many of the features on the Moon are named for astronomers. So are features on Mars and other planets and moons. And hundreds of asteroids are named for astronomers as well. But you won’t find many features named for astronomers here on Earth. Quite a few streets and schools are named after them. But when it comes to major features, the list is pretty thin – especially in the United States. One of the few is Mount Langley, a 14,000-foot summit in California. It’s named for Samuel Pierpont Langley, who was a long-time director of the Allegheny Observatory. To see more features named for astronomers, though, you need to head south – to Australia, New Zealand, and even Antarctica. In Australia, for example, a river and an estuary are named for Thomas Brisbane, an early governor of the state of New South Wales. And so is the city of Brisbane, the capital of Queensland. In addition to his government duties, Brisbane was an astronomer. He set up Australia’s first major observatory. In New Zealand, several peaks in a large mountain range are named for astronomers, including Galileo and Copernicus. And an entire range is named for Johannes Kepler. In Antarctica, many features are named for James Ross, an early explorer. But Ross himself named several features for astronomers, including Cape Smyth and Mount Lubbock – down-to-earth features named for men who studied the stars. Script by Damond Benningfield

When a dying Sun-like star exhales its final breath, it’s a doozy. The star blows its outer layers of gas into space. That surrounds the star’s dying core with a colorful bubble. The bubble can last for tens of thousands of years before it fades away. One of those bubbles is on the edge of Gemini, which is well up in the east at nightfall. Known as the Medusa Nebula, the bubble is about 1500 light-years away, and it spans more than four light-years. It’s named for one of the Gorgons of Greek mythology. That’s because some of its tendrils of gas have reminded skywatchers of the snakes on Medusa’s head. Those tendrils have been expanding into space for thousands of years. They began their journey when their star could no longer produce nuclear reactions in its core. Gravity squeezed the dying core tighter, making it smaller and hotter. The radiation of the hotter core pushed away the layers of gas around the core. Today, they’re moving outward at more than 30 miles per second. Ultraviolet light from the core “energizes” the gas in the nebula, making it glow like a fluorescent bulb. Different elements glow in different colors. That tells astronomers about the original star, and about the process of its demise. The fate of the Medusa Nebula is shared by all Sun-like stars. So billions of years from now, the Sun will create its own nebula – a colorful bubble blown with its dying breath. Script by Damond Benningfield

There just aren’t enough superlatives to describe the galaxy OJ 287. It’s a quasar – an especially bright object powered by two supermassive black holes. One of them is about 150 million times as massive as the Sun. The other is 18 billion times the Sun’s mass – one of the heaviest black holes yet seen. They team up to produce outbursts that are a trillion times brighter than the Sun – brighter than all the stars in the Milky Way Galaxy combined. OJ 287 is always bright. But every few years, it flares up – the result of interactions between the black holes. Each of them is encircled by a giant disk of gas. As the gas spirals in, it gets extremely hot. That makes the disks extremely bright. The smaller black hole orbits the larger one every 12 years. The orbit is tilted. So every six years, the black hole plunges through the disk around the larger black hole. That can heat some regions to trillions of degrees, producing the flare-ups. Astronomers recently used radio telescopes to take a picture of the system. They saw a long “jet” of particles from the smaller black hole. The jet is twisted by the interactions between the black holes – confirming the profile of this amazing system. OJ 287 is in Cancer, which is low in the east at nightfall. Even though it’s billions of light-years away, OJ 287 is bright enough to see through most amateur telescopes. Script by Damond Benningfield

Saturn’s rings are among the most beautiful features in the solar system – and the most mysterious. Scientists continue to debate how and when the rings formed, and how much longer they might hang around. But the rings aren’t Saturn’s only beautiful and mysterious feature. An almost perfect hexagon of clouds wraps around the planet’s north pole. And scientists continue to debate how it formed and what keeps it going. Saturn is the second-largest planet in the solar system – nine-and-a-half times the diameter of Earth. So the hexagon is giant as well – more than twice as wide as Earth. And it’s long-lasting – it was first observed in 1981. There are several ideas about what shapes the hexagon. Perhaps the leading idea says that winds deep in the atmosphere blow at different speeds at different latitudes. As these jet streams rub against other, they create waves that ripple to the top of the clouds. Those clouds form regular patterns – the sides of the hexagon. There’s one other mystery about the hexagon: It appears only at the north pole, not the south. So scientists are still working to explain this beautiful feature at the top of a beautiful planet. Saturn poses near the Moon the next couple of evenings. It looks like a bright golden star. It’s to the upper left of the Moon tonight, and a bit farther below the Moon tomorrow night. Tomorrow: a system that defies description. Script by Damond Benningfield

Orion climbs high across the sky on winter nights. It’s in the east-southeast at nightfall, and it’s easy to pick out. Look for the constellation’s “belt” – a short line of three stars that points straight up. In ancient Greece and Rome, Orion was known as a mighty hunter. But in ancient Egypt, the figure was even mightier. It represented Osiris, the god of the underworld. In fact, he was thought to reside in the stars of the belt. The story of Osiris dates to Egypt’s Old Kingdom, at least 4500 years ago. It says that Osiris was a great king. But he was murdered and chopped apart by his brother, Set. Isis, Osiris’s wife and sister, recovered the pieces, wrapped him in bandages, and used a magic spell to resurrect him. She then gave birth to Horus, who avenged his father by killing Set. As a god, Osiris reigned over the underworld. When the Sun passed through the underworld at night, Osiris gave new life to the Sun god, Re. So he became known as the god of rebirth and resurrection. He was associated with the start of a new year, when the Nile brought lifegiving floods to the fields. When a king died, he joined Osiris in the stars. Some researchers have suggested that a shaft in the Great Pyramid of Giza aimed toward Orion’s Belt at the time it was built. Others say there’s no astronomical significance to the shaft. But just about everyone agrees that Orion’s Belt was considered the resting place of Osiris. Script by Damond Benningfield

Orion is a land of monsters. It’s packed with stars that are among the most impressive in the galaxy – they’re big, heavy, and bright. Even among all those superstars, though, Lambda Orionis stands out. It consists of two monster stars. The largest is about 35 times the mass of the Sun, and perhaps 200 thousand times brighter. Orion is home to so many major stars because it’s on the leading edge of a spiral arm – a zone where many new stars are being born. Lambda belongs to a cluster that’s one hotbed of starbirth. It contains many stars of all sizes and masses. Lambda’s main star is the brightest and heaviest in the cluster. The cluster is encircled by a ring of gas and dust – probably outlining the shockwave of a massive star that exploded as a supernova. Lambda’s radiation zaps the material in the ring, making it glow. Lambda is only a few million years old, yet its time is almost up. Because it’s so massive, it will live a very short life. Soon, it may explode as a supernova, with its core collapsing to form a black hole. On the other hand, it might be massive enough for the entire star to become a black hole, with no explosion at all – a monstrous ending for a monster star. Orion is in the east and southeast at nightfall. Bright orange Betelgeuse marks its left shoulder. Lambda is to the upper right. Despite its true brilliance, it looks fainter than many of the hunter’s other impressive stars. Script by Damond Benningfield

For a while now, astronomers have suspected that Betelgeuse has a companion. And they might have found it. If it really exists, though, it won’t be around for long. Betelgeuse is a supergiant. It’s about 15 times as massive as the Sun, hundreds of times wider than the Sun, and tens of thousands of times brighter. There’s a wobble in the star’s light that lasts about six years – possibly caused by the gravity of a smaller companion star. A team looked for the companion in 2020 and 2024. The team stacked thousands of short-exposure images together, producing a sharp view of the system. The researchers didn’t see anything in 2020 – but they hadn’t expected to. The two stars were predicted to be too close together to tell them apart. But the team did see the companion in 2024, when the stars were farther apart. If the star really exists, it would be a little bigger and heavier than the Sun. But it’s so close to Betelgeuse that it’s enveloped in the supergiant’s outer atmosphere. That’s pulling the star closer in. Eventually, it should get so close that the gravity of Betelgeuse will rip it apart. And even if that doesn’t happen, before long Betelgeuse will explode as a supernova – bad news for both stars. Betelgeuse is the bright orange shoulder of Orion the hunter. It’s a third of the way up in the east-southeast at nightfall, to the left of Orion’s Belt. More about Orion tomorrow. Script by Damond Benningfield

A research paper published a couple of years ago featured an ominous title: “The Death of Vulcan.” A team of astronomers killed off a possible planet around the star 40 Eridani. In the lore of Star Trek, the star is the home of the planet Vulcan. 40 Eridani is actually a triple star. The main star is the one that’s supposed to host Vulcan. It’s a little smaller and lighter than the Sun, and only about 40 percent as bright. It’s probably older than the Sun, so there’s been plenty of time for life to develop on any planets that orbit the star. And in 2018, astronomers reported the possible discovery of one. The planet would have been a “super-Earth” – about eight times Earth’s mass. But the discovery was tentative. And several follow-ups found little evidence to support it. One concern was that the planet appeared to orbit the star once every 42 days. But that’s about the same period as the star’s rotation. And according to the 2024 study, that’s no coincidence. The earlier study had actually detected activity on the surface of the star. That activity looked like the signal of an orbiting planet. So a possible planet Vulcan vanished in the starlight. 40 Eridani is in the constellation Eridanus, the river. The star is in the southeast at nightfall, well to the upper right of Orion’s Belt. Under dark skies, the star is visible to the eye alone. Script by Damond Benningfield

Epsilon Eridani is the third-closest star system that’s visible to the unaided eye – just 10 and a half light-years away. It was among the first stars found to be encircled by a disk of dust. And it was one of two stars targeted in the first search for radio signals from other civilizations. The star itself is a little smaller and lighter than the Sun, and only a third as bright. It’s also billions of years younger than the Sun. Younger stars generate stronger magnetic fields. So Epsilon Eridani produces bigger magnetic storms than the Sun does, plus a much stronger “wind.” In 1983, a satellite discovered that the star is surrounded by a wide disk of dust. Later observations found several asteroid belts – bands filled with big chunks of rock and ice. Over the decades, astronomers have reported several possible planets. But only one of them has stuck. The planet is similar to Jupiter, the giant of our own solar system. In 1960, the star was considered a good candidate to host another civilization. So when Frank Drake launched Project Ozma to listen for radio signals, Epsilon Eridani was one of his two targets. He didn’t hear a peep – and neither has any search since then. Epsilon Eridani is well up in the south at nightfall, far to the right of the top right corner of Orion. The star isn’t all that bright, so you’ll need a starchart to pick it out. More about Eridanus tomorrow. Script by Damond Benningfield

The stars on the rim of the galaxy are going for a ride. They’re bobbing up and down like the horses on a merry-go-round. They’re also rippling outward, away from the center of the Milky Way. The Milky Way consists of a thin disk of stars and gas that spans a hundred thousand light-years or more. For decades, we’ve known that the rim of the disk is warped like the brim of a wide hat. It’s bent upward on one edge, and downward on the opposite edge. A recent study found that stars on those edges are moving along a big wave. Astronomers looked at the locations and motions of more than 20,000 bright young stars logged by the Gaia space telescope. The stars are as much as 45,000 light-years from the galactic center. Gaia found that the stars are bobbing up and down as much as a thousand light-years above or below the plane of the galaxy. And they appear to be sliding outward at thousands of miles per hour. The wave might have been created by a close approach of a smaller galaxy hundreds of millions of years ago. Its gravity disturbed the tranquility of the Milky Way’s outer precincts – sending the stars there for a ride. Under dark skies, the Milky Way is in good view tonight. In early evening, it extends along the body of Cygnus, the swan, in the west-northwest; through M-shaped Cassiopeia, higher in the sky; then down between Orion and the twins of Gemini, in the east-southeast. Script by Damond Benningfield

Almost 11 million years ago, a large asteroid slammed into Earth, somewhere around Australia. It could have gouged a crater more than 15 miles wide, and devastated life across tens of thousands of square miles. So far, though, the only traces of it are 14 tiny glass beads. Combined, they weigh just 53 grams – as much as a slice of bread. The beads are known as tektites. They formed from melted rock and sand that was blasted into the sky. Tiny blobs were shaped into balls by their passage through the air. Tektites are found all across the planet. Most of them are associated with a few major impacts. The region where a group of related tektites is found is called a strewn field. Five confirmed fields had been identified. One of them stretches across Australia and Asia. Decades ago, scientists identified eight tektites as members of that field, which was created by an impact about three-quarters of a million years ago. But a recent analysis found otherwise. Scientists conducted extensive studies of those beads, along with six others. They found that the beads were related to each other – but not to the known strewn field. Instead, they formed a new field, which stretches almost 600 miles across Australia. The beads are all the same age. So they formed in the same impact – 11 million years ago. But no one has yet found a crater – only a tiny handful of beads from a possible cosmic impact. Script by Damond Benningfield

Farmers in the American breadbasket are used to weather troubles: floods, droughts, hail, and more. But a storm in May of 2024 was something new. It caused machinery to go haywire during the peak of planting season. That caused an estimated 500 million dollars in losses. What was different about this storm was its source: the Sun. Massive outbursts of particles and energy bombarded Earth. That caused impressive displays of the northern lights. But it also messed with GPS satellites. From the central United States, GPS positions were off by more than 200 feet. That messed with farm equipment, disrupting the planting. A recent study said that such breaks could be more common in the decades ahead. The Sun goes through an 11-year cycle of storms. Big storms can cause all kinds of problems for modern technology. A couple of recent cycles were unusually quiet. And forecasts had called for the same from the current cycle, which peaked in 2024 and ’25. But those forecasts were wrong. The current cycle has been much more active than the previous ones, with many more sunspots than expected, and many more big outbursts. The recent study said that upcoming cycles could be even busier. The solar wind has been getting stronger since 2008 – an indication that the Sun is waking up from a “sleepy” period. So farmers – and the rest of us – could see more space weather problems in the decades ahead. Script by Damond Benningfield

Earth is getting fainter. For proof, just look at the Moon – something that scientists have been doing for decades. They’ve been looking at earthshine – sunlight reflected off of Earth. We see it lighting up the nighttime portion of the Moon – the part that’s not brightly lit by the Sun. It gives that part of the Moon a ghostly appearance. Right now, most of the lunar hemisphere that faces our way is in earthshine. The Moon is a thin crescent in the early morning sky. It’s getting thinner by the day as it wanes toward “new.” From the Moon, though, Earth is getting fatter. It’ll be “full” in just a couple of days. How bright Earth looks varies a good bit, depending on the exact distance, the amount of ice and cloud cover, and other factors. Clouds and ice are bright; land and oceans are dark. So as Earth turns on its axis, and different features rotate into view, earthshine goes up and down like a dining room light on a rheostat. Earthshine varies over longer periods as well, as a result of Earth’s changing climate. If cloud and ice coverage goes down, so does Earth’s overall brightness. And several studies have reported that that’s just what’s happening. Earthshine isn’t as bright as it was decades ago. The difference is small but clear – providing slightly darker nights on the Moon. Look for the Moon low in the sky before dawn tomorrow. The bright star Antares, the heart of the scorpion, is close by. Script by Damond Benningfield

Mighty Orion the hunter has a mighty resting spot for his tired feet: Cursa, the second-brightest star of Eridanus, the river. The star’s name comes from a longer Arabic phrase meaning “footstool of the central one” – Orion himself. As night falls, the star stands above Orion’s foot: Rigel, the hunter’s brightest star. Cursa is about 90 light-years away. It’s easy to see from that distance because it’s a giant. It’s several times the size and mass of the Sun, and 45 times the Sun’s brightness. Its classification as a “giant” tells us much more than just its size, though. It also tells us about its stage in life. A giant star has puffed up as a result of changes deep in its heart. It’s burned through the hydrogen in its core to make helium, so it’s moved into a new phase. In the case of Cursa, it’s fusing hydrogen in a thin shell around the core. The shell is quite hot, so it produces a lot of radiation. That pushes on the surrounding layers of gas, causing the star to expand. And that makes it brighter. Today, the surface of Cursa is thousands of degrees hotter than the Sun’s. At that temperature, the star shines almost pure white. As it continues to change, though, Cursa may get even bigger and brighter. But its surface will get cooler. So a bigger Cursa will shine redder – an angry-looking footstool for the hunter. Tomorrow: from giant to supergiant. Script by Damond Benningfield

Earth passed by Jupiter yesterday. Now, we’re beginning to leave the giant planet behind. We’ll loop past it again early next year. That passage is known as opposition – Jupiter lines up opposite the Sun in our sky. It’s closest to us then, so it shines brightest for the year. And it’s in view all night. Jupiter is much farther from the Sun than Earth is, so it takes about 12 years to complete a single orbit. Earth follows a much shorter path around the Sun, and it moves faster. So it passes Jupiter every 13 months. As we approach Jupiter, the planet stops its normal eastward motion against the background of stars. For a while, it moves backward – a period known as retrograde. Jupiter itself doesn’t change direction. Instead, the shift is a result of our changing viewing angle. It’s like passing a car on the highway. For a little bit, the other car looks like it’s moving in reverse compared to the background of buildings and trees. As the gap opens, though, it appears to resume its forward motion. Jupiter will reach that point on March 11th – shifting gears as it circles the Sun. Jupiter looks like a brilliant star – brighter than any other planet or star in the night sky now. The twin stars of Gemini are close by. Pollux, the brighter twin, is close to the left of Jupiter at nightfall. Castor is farther to the upper left. The whole group soars high across the south during the night. Script by Damond Benningfield

The closer we look at the worlds of the solar system, the more places we see that could be homes for life. Some of those worlds orbit Jupiter, the largest planet in the solar system. Jupiter itself isn’t on the list. It’s a big ball of gas with no solid surface. There has been speculation that large organisms could float through its skies. But that’s considered a long shot. It’s more likely that life could inhabit some of Jupiter’s moons. The leading candidate is Europa. It’s about the same size as our own moon. A deep ocean of liquid water probably lies below its icy crust. Plumes of hot water may squirt into the bottom of the ocean. The plumes would contain a variety of compounds – perhaps including the chemistry of life. So Europa has the right combination of water, heat, and chemistry to support life – at least microscopic life. Europa isn’t the only Jovian moon with a deep ocean. The largest moon, Ganymede, may have more liquid water than all Earth’s oceans combined. One other big moon may have an ocean as well. But the crusts of these moons are much thicker than Europa’s. So even if their oceans are inhabited, it’ll be much harder for us to find evidence of life. Look for Jupiter in the eastern sky in early evening, and arcing high across the sky later on. It looks like a brilliant star. Through binoculars, its big moons look like tiny stars quite close to the planet. More about Jupiter tomorrow. Script by Damond Benningfield

Jupiter looks like it’s wearing zebra stripes. Bands of clouds that run parallel to the equator alternate between bright and dark – zebra stripes. Each one is thousands of miles wide. The stripes are a result of Jupiter’s composition and its rotation. It’s basically a ball of gas – it’s made almost entirely of hydrogen and helium. And even though it’s 11 times the diameter of Earth, it spins on its axis in less than 10 hours. That forces the clouds that top its atmosphere into bands that stretch from east to west. The bands alternate between belts and zones. The belts are darker – probably because they allow us to see deeper into the atmosphere. The zones are topped by the highest clouds. The clouds are made of frozen ammonia, which looks bright white. The belts don’t have that layer. Instead, we’re seeing clouds in the next layer down. Those clouds are made of water and other compounds, which are darker. The stripes are flanked by jet streams that blow in alternating directions. They can roar at hundreds of miles per hour. They keep the belts and zones separated – maintaining the zebra stripes on this giant planet. Jupiter is at its best this week. It’s in view all night, and it shines brightest for the year. It looks like a brilliant star. It’s low in the eastern sky in early evening, and climbs high across the sky later on. The stripes are easily visible through just about any telescope. Script by Damond Benningfield

If today is your birthday, then Happy Birthday! The next one is just one year away – 365 sunrises and sunsets. If today is your birthday and you happen to be from Jupiter – well, Happy Birthday, and … we’re sorry. Your next one is almost 12 Earth years away – almost 10,500 sunrises and sunsets. The Jovian year is so long for a couple of reasons. First, the planet is more than five times farther from the Sun than Earth is. So its path around the Sun is more than five times longer than Earth’s. The second reason is the laws of orbital motion. The farther a planet is from the Sun, the slower its orbital speed. At Jupiter’s great range, it moves at less than half the speed of Earth. Ergo, one Jovian year lasts almost 12 Earth years. But to get all those sunrises and sunsets, you also have to factor in the length of a Jovian day. Although Jupiter is 11 times the diameter of Earth, it spins in a hurry – a day lasts less than 10 hours. Add it all up, multiply, divide, and carry the two, and – well, it’s a lot of days between birthdays on the Sun’s largest planet. Jupiter is especially vibrant now. It reaches opposition this weekend – it lines up opposite the Sun in our sky. It rises around sunset and is in view all night. The planet is also closest to us, so it shines at its brightest. In fact, in all the night sky right now, only the Moon outshines it. More about Jupiter tomorrow. Script by Damond Benningfield

Stars are born when giant clouds of gas and dust break apart and collapse. And if that’s all there was to it, the Milky Way Galaxy would give birth to a couple of hundred stars every year. Instead, thanks to feedback from the stars themselves, it makes only a few. Feedback is a process that clears away the material for making stars, but can also trigger the birth of more stars. Young stars, for example, produce winds and jets that blow away the gas and dust around them. Since stars are born in clusters, many youngsters can be sweeping away the star-making material at the same time. That pares back the number of stars that can be born in a cluster. Mature stars add to the feedback – not only with winds, but also with radiation. Hot stars generate a lot of ultraviolet energy. It vaporizes tiny particles of dust – eliminating possible building blocks for new stars. The heaviest stars explode as supernovas. These blasts can clear out the space for light-years around, creating big, empty bubbles. And supernovas also accelerate subatomic particles around them to almost the speed of light. These “cosmic rays” help to sweep away the raw material for making more stars. But supernovas can also enhance the birth rate. Their shock waves can cause distant clouds of gas and dust to collapse to form stars. So feedback is a complex process – one that both aids and hinders the birth of new stars. Script by Damond Benningfield

The planet Venus is switching sides today – sides of the Sun. It’s crossing behind the Sun as seen from Earth, so it’s moving from the morning sky to the evening sky. But we won’t be able to see it for several weeks. Venus is the second planet from the Sun, while Earth is third. So Venus crosses both behind the Sun and between Earth and the Sun. It switches between Morning Star and Evening Star appearances each time. Each of these crossings happens every 584 days – about 19 and a half months. The planet spends about eight months in both the morning and evening sky, and disappears from view during the crossings. When Venus passes between Earth and the Sun, it’s closest to us, so it moves across the sky quickly – it’s hidden in the Sun’s glare for only a few days. When it’s behind the Sun, it’s farthest – about 160 million miles. Because of the relative motions of Earth and Venus, it moves across the sky quite slowly. So it remains hidden in the light for three months or so. Depending on your location, Venus could emerge as the Evening Star as early as mid- to late February. It’ll be quite low in the twilight, so it won’t be easy to find. The planet will climb into better view in early March. Venus will reign over the evening sky until October, when it will vanish in the sunlight as it once again switches sides. Tomorrow: slowing down the stellar birth rate. Script by Damond Benningfield

The gibbous Moon soars across the sky tonight. It’s about three days past full, so the Sun lights up about 90 percent of the lunar hemisphere that faces our way. That makes the Moon nice and bright. But it’s not as bright as you might expect. In fact, it’s only about half as bright as the full Moon. There are a couple of reasons for that. One is our viewing angle. The full Moon stands opposite the Sun in our sky, so the sunlight that strikes it is reflected straight back toward Earth. That makes the Moon a more efficient mirror. But the main reason is the shadows. At full Moon, the shadows on most of the visible surface are short. In fact, there are almost no shadows at all across the center of the lunar disk. But as the Moon moves in its orbit around Earth, the angle between the Sun and Moon changes. The Sun drops lower in the lunar sky, so the shadows grow longer as seen from Earth. More shadows mean a darker surface. Despite appearances, none of the Moon is especially bright. It reflects only a bit more than one-tenth of the sunlight. It looks so bright only because it’s a close, big presence – lighting up the night sky. A bright star joins the Moon tonight: Regulus, the heart of the lion. It’s below the Moon as they climb into good view, about 9 or 9:30. The Moon will slide toward the star during the night, and they’ll be especially close as the dawn twilight begins to erase the star from view. Script by Damond Benningfield

There’s no fountain of youth to make people look younger. But there is one for stars. It’s a process that sounds like something from a horror movie – “stealing” life from another star. A good example is in Fornax, the furnace, which is low in the south at nightfall. The constellation has only one moderately bright star, Alpha Fornacis. It’s 46 light-years away. To the eye alone, it’s not much to look at. But binoculars reveal two stars. One of them is bigger and heavier than the Sun. Because of its greater mass, it’s nearing the end of its life, even though it’s almost two billion years younger than the Sun. The other visible star is smaller than the Sun, and its surface is cooler, so it glows orange. Yet it should be even redder than it is. And that’s where the story of rejuvenation comes in. The star is a blue straggler. That means its color has shifted to bluer wavelengths. That might be because it merged with another star. The merger would rev up the nuclear reactions in its core, making it hotter and bluer. On the other hand, it might have changed color by simply stealing gas from a third star in the system. This extra star was discovered in 2016. It’s a white dwarf – a stellar corpse. It’s about half as massive as the Sun, and it’s quite close to the blue straggler. So the straggler might have siphoned away the star’s life – taking some of its gas to “rejuvenate” its own appearance. Script by Damond Benningfield

The Moon sometimes rumbles during “moonquakes.” And according to a recent study in China, those quakes may happen fairly often. The first moonquakes were recorded by instruments left on the lunar surface by Apollo astronauts. Some of the quakes are deep – they’re centered hundreds of miles below the surface. They’re triggered by the tides – the gravitational pull of Earth squeezes and stretches the interior, causing things to clatter about. The other main moonquakes are shallow – they occur much closer to the surface. These quakes are triggered by the Moon itself. Our satellite world is shrinking as it loses its internal heat. It might have shrunk by as much as 150 feet over the past few hundred million years, and continues to contract even today. The Chinese study looked at 74 spots on the lunar surface, on both the nearside and farside. Scientists pored over hundreds of pictures snapped from 2009 to 2024. And they found 41 fresh landslides that happened during that period. They ruled out other causes for about 70 percent of the landslides. That left them with one conclusion: the landslides were caused by shallow moonquakes. So the Moon continues to shake and jiggle long after its birth. The Moon has some prominent companions tonight. It’s flanked by the brilliant planet Jupiter and the star Pollux, the brighter “twin” of Gemini. Castor, the other twin, is to the upper left of the Moon. Script by Damond Benningfield

Nothing symbolizes a cold, moonlit night like the howl of a wolf. The haunting sound can travel for miles. And if you live around wolf territory, you might especially notice it tonight. There’s a full Moon – the Frost Moon, Moon After Yule, or Wolf Moon. Despite what you might think, though, the wolves aren’t actually howling at the Moon. Many cultures have associated wolves and the Moon – ancient Moon goddesses often were depicted hanging with wolves. And biologists say that wolves may howl more around the time of the full Moon. But that’s only because they’re creatures of the night, so they’re more active when there’s more moonlight. Wolves communicate with each other in many ways besides howling. They growl, bark, and whimper. Each method conveys a different type of message. And howls can have different meanings, too – conveyed through changes in pitch, duration, and frequency. The howls help them attract mates, coordinate their hunting, and warn members of other packs to stay away. There’s even a “lonesome” howl when a wolf gets lost. Wolves do tilt their heads up when they howl – as though they were talking to the Moon. But there’s a practical reason – the sound carries farther. So if you happen to hear the lonesome howl of a wolf under the light of the full Moon, enjoy the serenade – just don’t think the wolf is howling at the Moon. Script by Damond Benningfield

At the dawn of the 19th century, the celestial police were on patrol. They were looking for a planet between the orbits of Mars and Jupiter. And on the century’s first day, a future squad member found one – sort of. Later discoveries showed that it wasn’t a planet at all, but the first and largest member of the asteroid belt – a wide band of millions of rocky bodies. Astronomers were looking for a planet because of the numbers. There seemed to be a mathematical relationship between the distances from the Sun to the known planets. But there was a gap between Mars and Jupiter. So one astronomer began organizing a search party: the celestial police. Giuseppe Piazzi, at the Palermo Observatory in Sicily, was on the list of people to invite. But he was already searching on his own. And before he got his invitation, he found something – 225 years ago today. Piazzi originally thought it was a comet – but hoped for something bigger. As other astronomers began studying it, they decided it was the sought-after planet. They named it Ceres, for the Roman goddess of agriculture. Within a few years, though, they’d found several other bodies in similar orbits. So they realized that Ceres wasn’t a planet at all, but just one member of a band of debris – the asteroid belt. Today, Ceres has regained its planetary status – sort of. It’s a dwarf planet – the only one in the inner solar system. Script by Damond Benningfield

By the time the ball drops in Times Square tonight, the people of the Line Islands will be almost a full day into 2026. The islands are in the Pacific Ocean, south of Hawaii. But they’re just across the International Date Line. That makes the islands the first place to see the new year. The Date Line is needed because the time gets an hour earlier for every time zone west, and an hour later for every time zone east. Without a place to reset the date, time just wouldn’t make sense. The line mostly runs down the middle of the Pacific – half way around the globe from Greenwich, England, which is the starting point for the time system. But individual countries can set their own time zones. So the line zigzags between Alaska and Russia. And near the equator, it jumps more than a thousand miles to the east. That extension came three decades ago. The island nation of Kiribati changed its time zones. That made it easier for the country to do business with Australia, which is west of the Date Line. The country’s easternmost extension is the Line Islands. So the date changes there first – making the Line Islands the first places on Earth to ring in the new year. American Samoa is farther west than the Line Islands. But its time zone puts it on the opposite side of the Date Line – making it one of the last places to change the calendar. Script by Damond Benningfield

The Sun and similar stars are losing weight – they blow some of their gas into space through strong “winds.” And at the end, they blow away all of their outer layers of gas. That leaves only their hot, dense cores, known as white dwarfs – tiny remnants of their once brilliant selves. An example is Sirius B, the faint companion of Sirius A, the brightest star in the night sky. Sirius climbs into view in the east-southeast by around 8:30 or 9, and arcs across the south during the night. Sirius B is too small and faint to see without a telescope. But long ago, that wouldn’t have been the case. The star probably was a few times as massive as the Sun, so it would have shined brighter than Sirius A is today. Such a hot, bright star produces a much thicker wind than the Sun does, so it loses mass at a higher rate. And because Sirius B was heavier than the Sun, it burned through the nuclear fuel in its core much faster – it fizzled out in a couple of hundred million years, while the Sun is still only half way through its 10-billion-year lifetime. As it neared the end of its life, Sirius B puffed up like a giant balloon, then ejected its outer layers. Some of that gas probably piled on the surface of Sirius A, increasing its mass. Today, Sirius B is as heavy as the Sun, but only as big as Earth. It still shines because it’s extremely hot. But it’s only a faint reminder of its former glory. Tomorrow: an early new year. Script by Damond Benningfield

Over the centuries, we’ve given all the visible stars many names – proper names, catalog designations, and others. But only one star is best known not by any of its formal names, but by its nickname: the Dog Star. Its proper name is Sirius, and it’s the leading light of the constellation Canis Major, the big dog – hence the nickname. Sirius is so well known because it’s the brightest star in the night sky – its closest competition is only about half as bright. Part of that is because Sirius itself is a couple of dozen times brighter than the Sun. But part of it is because Sirius is one of our closest neighbors – less than nine light-years away. And thanks to the relative motions of Sirius and the Sun, Sirius is moving closer, at about 12,000 miles per hour. It’ll continue to close in for tens of thousands of years. But the distances between stars are so vast that even at that speed, Sirius won’t grow much brighter in our sky. Astronomers discovered the star’s motion toward us by measuring its Doppler shift – a slight change in the wavelength of its light. The Doppler shift also allowed them to measure the orbit of a faint companion – a stellar corpse known as a white dwarf; we’ll have more about that tomorrow. In the meantime, look for Sirius climbing into good view in the east-southeast by around 8:30 or 9. It’s directly below the three stars of Orion’s Belt, so you can’t miss it. Script by Damond Benningfield

The most important thing to know about a star is its mass – how heavy it is. Among other things, the mass reveals how long the star will live and how it will die. Measuring the mass of a single star is tough. It’s a lot easier to get the masses of stars in binary systems – two stars that orbit each other. An example is Menkalinan, the second-brightest star of Auriga. It’s a third of the way up the northeastern sky at nightfall, below the charioteer’s brightest star, Capella. Menkalinan’s two stars are so close together that we can’t see them as individual points. But breaking the system’s light apart reveals the presence of both stars. The stars orbit each other every four days, at about one-tenth of the distance from Earth to the Sun. Combined, those numbers reveal the system’s total mass. A couple of other numbers complete the picture. One is the angle at which we’re seeing the system. In the case of Menkalinan, that’s easy – the stars pass in front of each other, so we see the system edge-on. The other is the orbital motions of the stars. Plugging those numbers into the formula provides a precise mass for the individual stars. The stars of Menkalinan are almost identical. Each is more than twice the mass of the Sun. Each is also bigger and brighter than the Sun. So even though Menkalinan is more than 80 light-years away, it’s easy to see – the combined glow of two big, well-understood stars. Script by Damond Benningfield

Orion is climbing into prominence in winter’s evening sky. The hunter clears the eastern horizon by about an hour and a half after sunset. He’s led by his shield. It’s not as easy to see as his belt or other features. But the shield’s brightest star does stand out. Pi-3 Orion is in the middle of the shield – where Orion’s hand is holding it. The star is a little bigger, heavier, and hotter than the Sun. That makes it about three times brighter than the Sun. There are a couple of ways to look at that brightness: apparent magnitude and absolute magnitude. Apparent magnitude is how bright a star looks. In that scale, Pi-3 shines at about magnitude 3.2 – not especially bright, but bright enough to see under even most light-polluted skies. But that number doesn’t tell you the star’s true brightness. It might be especially bright, but it might also be especially close. So that’s where absolute magnitude comes in. It’s how bright a star would look at a distance of 10 parsecs – 32.6 light-years. If you lined up every star at that distance, you could easily tell which ones are truly bright. Pi-3 is just 26 light-years away. If you moved it out to 10 parsecs, it would shine at magnitude 3.65 – half as bright as it looks now. In fact, if you moved all the stars in the shield to that distance, Pi-3 would be its faintest member – a middling middle for the shield. Script by Damond Benningfield

Not many planetary spacecraft get to shower off. But the Cassini spacecraft did – more than once. It flew through plumes of ice and water vapor from Enceladus, a moon of Saturn. The encounters helped scientists confirm that an ocean hides below the moon’s icy crust. Enceladus is a little more than 300 miles in diameter – roughly the distance from Los Angeles to San Diego. Its surface is completely coated with ice. That makes it the most reflective large body in the solar system, so it looks bright white. Much of that ice comes from more than a hundred geysers near the moon’s south pole. They erupt from deep cracks in the crust. They contain water vapor, water ice, hydrogen, grains of salt, and other compounds. Much of this material falls back on the surface. The rest of it escapes into space, where it forms a thin ring around Saturn. The geysers erupt from a global ocean. It’s buried about 20 to 25 miles below the surface, and it could be 10 miles deep or more. Hot, mineral-rich water could flow into the ocean through fissures on its floor. So the ocean appears to offer all the ingredients for life: liquid water, minerals, and a source of heat. That makes Enceladus a high-priority target in the hunt for life beyond Earth. Saturn is near our own moon this evening. It looks like a bright star, shining steadily through the lunar glare. But you need a good-sized telescope to pick out Enceladus. Script by Damond Benningfield

A look at the evening sky is a nice way to wrap up your Christmas. It features the Moon, two bright planets, and some of the brighter stars in all the night sky. As twilight drains from the sky, the Moon is well up in the southwest. The Sun lights up more than a quarter of the lunar hemisphere that faces our way, so it’s a fat crescent. It’s waxing toward first quarter, on Saturday. The planet Saturn is to the upper left of the Moon, and looks like a bright star. It shines so brightly for a couple of reasons: It’s the second-largest planet in the solar system – more than nine times the diameter of Earth – and it’s topped by clouds that reflect much of the sunlight that strikes them. The only planet that’s bigger than Saturn is Jupiter, and it climbs into good view, in the east-northeast, by 7 or 7:30. In all the night sky right now, only the Moon outshines it. The “twin” stars of Gemini – Pollux and Castor – stand to Jupiter’s left and upper left. At the same time, the brilliant constellation Orion is off to the upper right of Jupiter. Look for its three-star belt aiming straight up from the horizon, flanked by orange Betelgeuse and blue-white Rigel. Taurus perches well above Orion. It’s marked by its bright orange eye, Aldebaran. And the Dog Star, Sirius, climbs into good view by 8 or 8:30, below Orion’s Belt. It’s the brightest true star in the night sky – a beautiful decoration for Christmas night. Script by Damond Benningfield

For a star, showiness comes with a price. The most massive stars are far brighter than their punier cousins. But they live much shorter lives. An example is Alpha Camelopardalis. It’s the third-brightest star of Camelopardalis, the giraffe. It’s dimmed by its great distance – about 5500 light-years – so you need a dark sky to see it. Even so, it’s one of the most remote stars visible to the eye alone. The star is impressive. It’s more than 30 times the diameter of the Sun, and almost 40 times the Sun’s mass. Because of that great heft, Alpha Cam “burns” through the nuclear fuel in its core in a big hurry. That makes its surface tens of thousands of degrees hotter than the Sun’s, so the star shines blue-white. The combination of size and temperature makes Alpha Cam more than 600,000 times brighter than the Sun. The price for that showiness is a short lifespan. Stars like the Sun live for billions of years. But Alpha Cam will stick around for only a few million years. So even though it’s only about two million years old, its days are numbered. Before long – astronomically speaking – it will expire. Just how it will go out isn’t clear. Its core may collapse to form a black hole, with its outer layers exploding as a brilliant supernova. On the other hand, the entire star may collapse, forming a heavier black hole – a dark ending for a dazzling star. Script by Damond Benningfield

If you’d like to know how dark your night sky is, then look high in the northeast after the Moon sets this evening for the stars of Camelopardalis, the giraffe. If you can see any of them, then congratulations – your sky is pretty dark. Light pollution wipes out the view for most Americans. The glare of street lights, billboards, and other artificial sources overpowers the stars. None of the stars of Camelopardalis, for example, is brighter than fourth magnitude, which is pretty faint. So unless you’re under dark skies, there’s not much to see. That’s a little misleading, though. The giraffe’s brightest stars are all stunners. They look so faint only because they’re so far away. The giraffe’s brightest star is Beta Camelopardalis – Beta Cam for short. It’s a huge, massive star that shines roughly 1600 times brighter than the Sun. But it’s about 840 light-years away, so it’s a faint dot in the night sky. The next-brightest star is CS Cam. It is a supergiant star that’s perhaps 75,000 times the Sun’s brightness. But it’s 3400 light-years away. And the third-brightest, Alpha Cam, is the most impressive of all: more than 600,000 times the Sun’s brightness. At a distance of 5500 light-years, it’s one of the most remote stars visible to the unaided eye – but only under especially dark skies. More about Alpha Cam tomorrow. Script by Damond Benningfield

Space agencies are talking a lot these days about sending people to the Moon – and even setting up permanent bases there. But you might not want to be on the Moon seven years from today. A space rock that’s half the size of an NBA arena has a slight chance of slamming into the Moon. Asteroid 2024 YR4 was discovered last year, two days after Christmas, when the asteroid had flown just half a million miles from Earth. Early observations gave it more than a three percent chance of hitting Earth on December 22nd, 2032. As astronomers tracked it longer, they ruled out that chance. Instead, they calculated that it’ll pass about 7,000 miles from the Moon. But there’s a 45-thousand-mile margin of error. So there’s a better than four percent chance that it will hit the Moon. 2024 YR4 is so far away right now that we can’t see it. It won’t return to view until 2028. Once it reappears, astronomers will refine their calculations. That probably will rule out the chance of an impact. But for now, we can’t know for sure. The asteroid is about 200 feet in diameter. That’s about the size of the asteroid that gouged the famous meteor crater in Arizona. So an impact on the Moon probably would form a big crater. Debris from the impact could travel hundreds of miles – cosmic missiles crashing across much of the Moon. Script by Damond Benningfield

Today is the December solstice – the start of winter in the northern hemisphere. It’s the darkest time of the year – many hours of darkness for watching the stars. But it’s also a great time for space science in Antarctica, where it’s daylight around the clock. NASA launches high-altitude balloons from a base near McMurdo Station, the continent’s largest settlement. Their payloads can keep an eye on the heavens for weeks as they circle around the south pole. When their work is done, they parachute to the ice. Scientists from the United States, Japan, and other countries hunt for meteorites in Antarctica. There aren’t more meteorites there, but on the ice, there’s a good chance that almost any rock came from beyond Earth. Over the decades, tens of thousands of meteorites have been found there. Astronomers take advantage of the daylight to repair and upgrade telescopes at the south pole. The collection includes instruments that study the “afterglow” of the Big Bang. The instruments can operate even in daylight, but the southern summer is the only time to do most of the maintenance work. The south pole also is home to IceCube – a collection of thousands of light detectors frozen in the ice. They look for neutrinos – particles that tell us about some of the most energetic events in the universe. IceCube can also operate all year – even under the midnight sun at the south pole. Script by Damond Benningfield